This invention relates to apparatus for, and methods of, sterilizing articles such as food, drugs and medical instruments and implements. The invention particularly relates to apparatus for, and methods of, sterilizing articles which have a relatively great thickness.
It has been known for some time that drugs and medical instruments and implements have to be sterilized so that they will not cause patients to become ill from harmful bacteria when they are applied to the patients. Systems have accordingly been provided for sterilizing drugs and medical instruments and implements. The drugs and the medical instruments and implements have then beam stored in sterilized packages until they have been ready to be used.
In recent years, it has been discovered that foods can carry harmful bacteria if they are not processed properly or, even if they are processed properly, that the foods can harbor such harmful bacteria if they are not stored properly or retained under proper environmental conditions such as temperature. Some of these harmful bacteria can even be deadly.
For example, harmful bacteria have been discovered in recent years in hamburgers and by one of the large hamburger chains. Such harmful bacteria has caused a number of purchasers of hamburgers from stores in the chain to become sick. As a result of the incident and several other similar incidents, it is now recommended that hamburgers should be cooked to a medium state rather than a medium rare or rare state.
Similarly, harmful bacteria have been found to exist in many chickens that are sold to the public. As a result of a number of incidents which have recently occurred, it is now recommended that all chickens be cooked so that no blood is visible in the cooked chickens.
To prevent incidents such as discussed in the previous paragraphs from occurring, various industries have now started to plan to sterilize foods before the foods are sold to the public. This is true, for example, of hamburgers and chickens. It is also true of fruits, particularly fruits which are imported from foreign countries.
In previous years, gamma rays have generally been the preferred medium for sterilizing various articles. The gamma rays have been obtained from a suitable material such as cobalt and have been directed to the articles to be sterilized. The use of gamma rays has offered certain disadvantages. One disadvantage is that sterilization by gamma rays is slow. Another disadvantage is that sterilization by gamma rays is not precise. This results from the fact that the strength of the source (e.g., cobalt) of the gamma rays decreases over a period of time and that the gamma rays cannot be directed in a sharp beam to the article to be sterilized. This prevents all of the gamma rays from being useful in sterilizing the articles.
In recent years, electron beams have been directed to articles to sterilize the articles. Electron beams have certain advantages over the prior use of gamma rays to sterilize objects. One advantage is that sterilization by electron beams is fast. Another advantage is that sterilization by electron beams is relatively precise. Sterilization by electron beams is relatively precise because the strength of the electron beam remains substantially constant even when the electron beam continues to be generated over a long period of time.
Sterilization by electron beams has a limitation which sometimes may possibly be significant. Electrons in the electron beams constitute mass. As the electrons in the beam travel through the article to sterilize the article, they are slowed and eventually stopped by the mass of the article. This limits the thickness of articles which can be sterilized by electron beams.
X-rays have been used to sterilize articles. X-rays are advantageous in that they have no mass. The x-rays are in the form of electromagnetic energy which penetrates the articles to be sterilized. Since the x-rays have no mass, they are effective in sterilizing articles with significant thicknesses. These significant thicknesses are considerably greater than the thicknesses of the articles which can be sterilized by other forms of energy such as electron beams.
There is one significant disadvantage, among others, in the use of x-rays to sterilize an article. This results from the fact that a considerable amount of energy remains in the x-rays after the x-rays have passed through the article. The energy remaining in the x-rays after the passage of the x-rays through the article has represented wasted energy because they are not used for any useful purpose.
In a preferred embodiment of the invention, articles having a considerable width are subjected to radiation. The widths of the articles are so great that x-rays are preferably used to provide the radiation. In a preferred embodiment of the invention, all of the x-ray energy is used to irradiate the articles, in contrast to the embodiments in the prior art. All of the x-ray energy is used efficiently in this manner without reducing the number of units which are processed per unit of time.
In the preferred embodiment, a first support structure disposes articles relative to a radiation beam, preferably x-rays, to obtain an irradiation of the articles by radiation passing from the beam through the articles on the first structure. A second support structure disposes articles relative to the beam and to the articles on the first structure to obtain an irradiation of the articles by radiation passing from the accelerator through the articles on the first structure. A mechanism transfers the articles on the first structure to the second structure, after the irradiation of the articles on the first structure, to obtain the irradiation of the articles on the second structure.
Each of the first and second structures may provide for an irradiation of the articles initially through first sides of the articles and subsequently through second sides of the articles opposite to the first sides. The irradiation of the first sides of the articles on the first and second support structures are preferably synchronous from a time standpoint as are the irradiations of the second sides of the articles on the structures. The transfer mechanism provides for the transfer of the articles from the first structure to the second structure after the synchronous irradiation of the second sides of the articles in the support structure.
A loading area transfers articles to the first structure for an irradiation of the articles by the x-ray radiation. An unloading area provides for a transfer of articles from the second structure after the irradiation of the opposite sides of the articles in the second structure.